Inkjet printing mechanisms use pens which shoot drops of ink onto a page. Each pen has a printhead formed with very small nozzles through which the ink drops are fired. To print an image, the printhead moves back and forth across the page shooting drops as it moves. To improve the clarity and contrast of the printed image, recent research has focused on improving the ink itself. For example, to provide darker blacks and more vivid colors, inks having a higher solid content than previous inks have been developed.
For example, the ink used in inkjet printers dries quickly, allowing these printers to use plain paper. However, the combination of small nozzles and quick-drying ink leaves the printheads susceptible to clogging, not only from dried ink or minute dust particles, such as paper fibers, but also from the solids within the new inks themselves.
Typically, a service station is mounted within the printer chassis, and serves to clean and protect the printhead. During operation, clogs in the printhead are periodically cleared by firing a number of drops of ink through each of the nozzles, with the waste ink being collected in a reservoir portion of the service station. This waste ink reservoir, which is often referred to as a "spittoon," has been a stationary device located adjacent to the nozzle caps and wipers of the service station. While stationary spittoons were suitable for the earlier inks, they suffer a variety of drawbacks when used with the newly developed inks, which have a higher solids content than the earlier inks.
Referring to FIG. 8, a vertical sectional view is shown of a conventional prior art spittoon S which has been receiving waste ink of the newer variety for a period of time. The rapidly solidifying waste ink has gradually accumulated into a stalagmite I. The ink stalagmite I may eventually grow to contact the printhead H, which could interfere with printhead movement, print quality, and/or contribute to clogging the nozzles. Indeed, stalagmites (not shown) may even form from ink deposits along the sides of the spittoon and they may grow to meet one another and clog the entrance to the spittoon. To avoid this phenomenon, conventional spittoons must be wide, often over 8 mm in width to handle a high solid content ink. This extra width increases the overall printer width, resulting in additional cost being added to the printer, both in material and shipping costs.
This stalagmite problem is particularly acute for a polymer or a wax based ink, such as an ink based on carnauba wax, or a polyamide. In the past, inkjet printers using polyamide-based inks have replaced the conventional spittoon of FIG. 8 with a sheet of flat plastic. The nozzles are periodically cleared by "spitting" the hot wax ink onto the plastic sheet. At regular intervals, an operator must remove this plastic sheet from the printer, flex the sheet over a trash can to remove the waste ink, and then replace the cleaned sheet in the printer. This cleaning step is particularly inconvenient for operators to perform on a regular basis.
The use of an operator-cleaned flexible sheet is not suitable for the new high solids ink. In comparison to the wax or polymer based inks, these new inks leave a waste which is quite dirty, due to the high amount of solids used to improve the contrast and quality of the printed images. Thus, operator intervention to regularly clean a high solids ink spittoon could lead to costly staining of clothing, carpeting, upholstery and the like.
Besides increasing the solid content, mutually precipitating inks have been developed to enhance color contrasts. For example, one type of color ink causes black ink to precipitate out of solution. This precipitation instantly fixes the black solids to the page, which prevents bleeding of the black solids into the color regions of the printed image. Unfortunately, if the mutually precipitating color and black inks are mixed together in a conventional spittoon, they do not flow toward a drain or absorbent material. Instead, once mixed, the black and color inks instantly coagulate into a gel, with some residual liquid being formed.
Thus, the mixed black and color inks have the drawbacks of both hot-melt inks, which have an instant solid build-up, and the aqueous inks, which tend to run and wick (flow through capillary action) into undesirable locations. To resolve the mixing problem, two conventional stationary spittoons are required, one for the black ink and one for the color inks. As mentioned above, these conventional spittoons must be wide to avoid clogging from stalagmites growing inward from the spittoon sides. Moreover, two spittoons would further increase the overall width of the printer, which undesirably adds to the overall size of the inkjet printer, as well as its weight and material cost to build.